In 2021, the residents in Vridsløsemagle, a small Danish village west of Copenhagen, got an offer to be supplied with district heating. It would be based on local extraction and distribution of shallow geothermal energy using a new-built thermonet. The residents until then mainly relied on oil boilers and wood stoves. The solution would be provided by Høje Taastrup Fjernvarme, which is one of Denmark’s largest consumer-owned district heating companies.

The system was established in 2023 with close to 60 connected consumers. Vridsløsemagle Village Association has played a crucial role in communicating and discussing connection possibilities with the village’s residents. The thermonet-system is dimensioned so that potentially all of Vridsløsemagle’s 110 households can be connected.

Vridsløsemagle’s new collective heating supply is by Høje Taastrup Fjernvarme described as “cold district heating” and it was established under the Danish heating supply act while this was still possible. It consists of 23 shallow geothermal boreholes, a piping network (the thermonet) and decentralized liquid-to-water heat pumps located in the connected houses.

The solution was chosen based on economic considerations. Vridsløsemagle is located approximately 4 km from Høje Taastrup Fjernvarme’s existing district heating network, so a traditional district heating project with long routing of insulated pipes would have been too costly due to the relatively small heating demand in the village.

Høje Taastrup Fjernvarme is one of approximately 280 Danish consumer-owned district heating companies. In EU terminology, the company can be described as an energy community. It deals solely with the supply of district heating and is regulated by a special Danish law, the heating supply act, which was originally passed in 1979.

Actors

Høje Taastrup Fjernvarme was the initiator, project manager and system owner.

Norsyn (formerly Damgaard Rådgivende Ingeniører) provided the engineering design.

Zacho-Lind supplied and established the thermonet including service lines. This was done with extensive use of horizontal directional drilling.

Bosch supplied the decentralized heat pumps in a special version with meters from Kamstrup for consumption reading purposes. Bosch handled the commissioning of the heat pumps.

GeoDrilling established the 23 vertical geothermal boreholes with Varup Termiske Boringer as the executing contractor. HakaGerodur has supplied thermal probes for the vertical boreholes.

Dantonit supplied a specially developed material used for borehole sealing.

VIA University College conducted a thermal response test to test the efficiency.

Priess supplied the central pump station that circulates the brine in the thermonet. The pump station was delivered factory-produced and tested. It was lifted into place using a mobile crane.

ENCO VVS Service handled installation and connection of the heat pumps.

Fløng EL handled connection of the pump station and heat pumps to the electrical grid.

The Solution

Høje Taastrup Fjernvarme has established local extraction of shallow geothermal energy. It is distributed via a thermonet (the piping network) to heat pumps located in the connected houses.

The heat is extracted from 23 vertical closed loop geothermal boreholes. Additionally, heat is extracted from the thermonet’s uninsulated pipes. The brine consists of water mixed with IPA alcohol for freeze protection, corresponding to what is normally used in ground source heat pump systems. Prior to establishment, an environmental assessment (EIA screening) was conducted to ensure that the system does not have harmful effects on the groundwater.

The heat pumps are installed in the connected houses where a district heating unit would normally be placed. They are owned, operated and serviced by the district heating company. In summer, the thermonet’s supply temperature is 5-10°C, while in winter it is around 0°C. Each decentralized heat pump provides a cooling of 5°C, meaning that the return temperature will be in the range +5°C to -5°C. The decentralized heat pumps deliver a supply temperature to the consumer’s heating system of minimum 60°C.

The thermonet has been largely established using horizontal directional drilling. This has reduced the inconvenience of construction work. Large-diameter PE pipes were delivered in 12 meter lengths, welded together on site and pulled into place in stretches up to 180 meters. Smaller diameter PE pipes were laid from rolls. The thermonet was placed in roads, including private shared roads.

The decentralized heat pumps are connected to separate electricity meters, which are billed by Høje Taastrup Fjernvarme. Høje Taastrup Fjernvarme also handles everything else regarding the collective heating supply, including:

• Establishment of service line to the property
• Installation and maintenance (the heat pump and the hot water tank)
• Setup of separate electricity meter and heat metering equipment
• Dismantling and disposal of existing heating systems.

The district heating company owns, establishes and operates both the boreholes, the thermonet and the decentralized heat pumps. The delivery boundary is the output side of the heat pump.

The potential annual heating demand for Vridsløsemagle’s 110 properties is calculated at 1,870 MWh. The only major consumer is a kindergarten. All other consumers are standard households with an average residential area of 135 sq m and an average heating demand of 16.6 MWh/year.

The thermonet is dimensioned for 585 kW and the supply need is estimated to be 475 kW. There is thus a 20 percent buffer.

The thermonet including service lines has a total length of approximately 4.3 km. Around the pumping station are use uninsulated PE pipes with diameter 280 mm. The main distribution pipes have a diameter of 160 mm, and the service lines’ diameter is 32 mm. The total length of extraction lines in the 200 meter deep heat boreholes amounts to 4.6 km of PE pipe with diameter 40 mm.

Economics

Consumers pay for heating consumption according to Høje Taastrup Fjernvarme’s applicable tariffs. Consumers in Vridsløsemagle who signed up before a set date were exempted from connection fees. Those who wish to connect later on must pay a connection contribution of approximately DKK 26,000 (2023 prices).

The cost for an average customer in Vridsløsemagle (135 sq m with an annual consumption of 16.6 MWh) amounts to DKK 11,230 per year. In addition, there is for Vridsløsemagle a special subscription for the heat pump of DKK 5,250 per year – thus a total of DKK 16,480 per year for an average customer (2023 prices).

Prior to establishment, a socioeconomic calculation was conducted according to the then applicable rules under the Danish heating supply act. It showed that there were both socioeconomic and user economic advantages to a district heating solution based on thermonet compared to establishing individual air/water heat pumps.

Key Experiences

It has been crucial for the project’s success that a district heating company took on the role of project owner and had it approved under the Danish heating supply act. This ensured stable and familiar frameworks around the district heating concept for consumers, including favourable financing conditions for the company. However, the Danish government amended the Heat Supply Act in 2024. Heating networks using thermonets and distributed heat pumps were exempted from the law and can no longer obtain the same favourable financing terms as traditional district heating solutions with centrally produced heat and insulated distribution pipes.

Throughout the entire process, Vridsløsemagle Village Association has played a central role as a collaborative partner for Høje Taastrup Fjernvarme.

The use of uninsulated PE pipes has eliminated the bottleneck regarding competent welders that would have existed if traditional district heating with insulated steel pipes had been established.

The use of horizontal directional drilling in Vridsløsemagle presented greater challenges than expected. This is due to the local geology with clay soil and many stones. This led to more excavation work than initially assumed.

The pricing model used, which fully corresponds to how district heating is priced in newly established supply areas, has made it easy to communicate the advantages of having a household connected from the start.

More information

• The project proposal (in Danish) as approved by Høje-Taastrup Municipality
• Energy Supply, May 5, 2022: Local district heating on the way to village in Høje-Taastrup Municipality (in Danish)
• Dansk Fjernvarme, March 9, 2023: Uninsulated pipes ensure district heating to Vridsløsemagle (in Danish)
• Sjællandske Nyheder, March 12, 2023: Here they get a new type of district heating (in Danish)
• Termonet Danmark, May 11, 2023: New district heating concept will be able to reach out to all villages (in Danish)
• Intelligent Energi, June 14, 2023: Many are eager for clarification about thermonet (in Danish)